Adopt: pdpv0 user-initiated termination (upstream PR#1246)

[Reiers]

Upstream PR: filecoin-project/curio#1246

Adds the POST /pdp/data-sets/{id}/terminate endpoint + supporting tasks for client-initiated dataset termination. Synapse-SDK already drives this via the FWSS contract; today curio-core has no termination path so a dataset created via curio-core can never be cleanly retired.

What to adopt:

• handler endpoint
• TerminationTask harmonytask
• DB schema (pdp_data_set_terminations table)
• FWSS requestTermination contract call wiring

Adapt for us:

• SQL port if PR uses any Postgres-specific syntax
• Schema goes into internal/harmonysqlite/schema-curio-core/

Tracks part of FilOzone/filecoin-services#484 ("FWSS support for simplified DataSet terminations").